Hydrodynamic Model with Binary Particle Diameters to Predict Axial Voidage Profile in a CFB Combustor

A hydrodynamic model with binary particle diameters was developed to better predict axial voidage profile in a CFB combustor. In the model, the CFB is regarded as a superposition of two sub-beds, a fast fluidized bed in the upper riser with a characteristic particle diameter of O.2mm and a bubbling fluidized bed or turbulent bed in the bottom riser with a characteristic particle diameter of 2mm. Furthermore, a variable critical particle diameter whose terminal velocity equals to the superficial gas velocity was employed to determine which flow regime the particle belongs to. The results show that binary particle diameter model has the advantages in describing wide particle diameter distribution while reducing the complexity of computation. The model was verified by the field data of voidage profile in a 300MW CFB boiler.